1. Field of the Invention
The present invention relates to a print head and an ink jet printing apparatus for using the print head, and particularly to a configuration for ink refill that is carried out in liquid paths of the print head in associated with ink ejection.
The present invention is applicable to general printing apparatuses, apparatuses such as copy machines, facsimile machines having a communication system, and word processors having a printing section, as well as industrial printing apparatuses combined with various processing apparatus in a compound manner.
2. Description of the Prior Art
Conventional printing apparatuses for printing data on printing medium such as a paper, a cloth, a plastic sheet, an OHP sheet or the like (hereafter simply referred to as xe2x80x9cprinting paperxe2x80x9d) are provided in a form of using a print head of various printing methods, for example, a wire dot method, a thermal-sensitive method, a thermal transfer method and an ink jet method.
The ink jet printing method carries out printing by ejecting an ink from fine openings for ink ejection (hereafter referred to xe2x80x9cejection openingsxe2x80x9d) of a print head and depositing the ink on printing paper in accordance with printing information. This method has various advantages of enabling printing at a relatively high speed and enabling printing on plain paper easily.
In addition, the ink jet method can be roughly classified depending on an ink droplet forming method and an ejection energy generating method into the continuous method (including a charge grain control method and a spray method) and a on-demand method (including a piezo method, a spark method, and a bubble jet method).
The continuous method is what ejects continuously a charged ink and controls electric fields to deposit only required ink droplets on printing paper. Also, the method collects in an ink receiver part of the ink which is not required for printing. In contrast, the on-demand method is what ejects an ink as required for printing and thus efficiently uses the ink while avoiding ejecting an unnecessary ink to prevent an inside of the apparatus from being stained. On the other hand, the on-demand method employs an ink ejection operation basically including a start and a stop operations of an ink flow, and thus has a lower response frequency for driving of the head than the continuous method. Thus, a number of ejection openings is increased to improve a printing speed as a whole. Based on above points, many of the currently available ink jet printing apparatuses are based on the on-demand method.
A printing apparatus of such an ink jet method has a printing head that comprises ink ejection openings, liquid paths each in communication with a corresponding one of the ink ejection openings and ejection energy generating elements for generating energy in the corresponding liquid path to eject the ink. To carry out printing, the ejection energy-generating element is allowed to generate ejection energy to act on the ink in the corresponding liquid path to generate a pressure therein for ejection, so that the pressure is then used to eject the ink from the ejection opening.
The ink used for the ink jet printing is commonly a printing agent such as a pigment or a dye which is dissolved or dispersed into a solvent such as water, a water-soluble organic solvent, or a non-water-soluble organic solvent.
In an ink ejection operation performed in the print head described above, the pressure generated for ejection is transmitted via the ink in the liquid path both toward the corresponding ejection opening for ejection and toward a liquid chamber that supplies the ink to the liquid path. A part of the pressure which is transmitted toward the ejection opening pushes the ink in the liquid path out from the ink ejection opening to form a flying droplet.
When ejected ink leaves the ink ejection openings in a form of droplet, a meniscus which is formed in the liquid path near the ejection opening moves back depending on an amount of the ejected droplet. A tension of the ink (capillary force) which pulls back the meniscus toward the ejection opening causes a filled state of the ink in the liquid path to be returned to that before the ejection after a certain amount of time has passed. This phenomenon is called xe2x80x9crefillxe2x80x9d, and in actual printing, the above operation is repeated to achieve appropriate refill to enable stable persistent ink ejection.
The refill, however, may fail to be completed before the next ejection due to a cause associated with an ejection frequency or the like, and this incomplete refill may result in inappropriate ejection such as a reduced amount of the ejected ink droplet. As a result, for example, a size of ink dots formed with the ejected ink droplet on a printing medium is reduced to degrade general printing quality and an accuracy with which the ejected ink droplets land on the printing medium, causing blurred, rumpled, striped, or whitened images to be printed.
In printing techniques such as the ink jet printing method which use liquids, the above described problem has been solved by improving structures such as the liquid path or adjusting physical properties of the ink. Mere such improvements or adjustments, however, often fail to sufficiently improve a print head with a large number of ink ejection openings. This problem will be described below with reference to drawings.
FIGS. 20A and 20B are views showing cross sections of main parts of an ink jet print head as seen from an ink ejection direction. FIG. 20A is a view useful in explaining a pressure caused upon ink ejection and acting toward a common liquid chamber, and FIG. 20B is a view useful in explaining a pressure required to obtain an appropriate refill state.
A print head 100 comprises a large number of ejection openings (not shown), liquid paths 102 each in communication with a corresponding one of the ejection openings, ejection energy generators 103 each disposed in a corresponding one of the liquid paths 102, and a common liquid chamber 104 for supplying an ink to each of the liquid paths. The common liquid chamber 104 is in communication with an ink tank (also referred to as an xe2x80x9cink cartridge,xe2x80x9d not shown) via an ink supply port 105 and is thus constantly filled with the ink.
As shown in FIG. 20A, when the inks are ejected from the large number of ink ejection openings 101 simultaneously or with a delay between ejection timings, a pressure caused by the ejection in each of the liquid paths 102 is transmitted therefrom toward the common liquid chamber 104. These pressures are integrated together in the common liquid chamber 104 to form a single high pressure. The pressures caused in each liquid path act as forces that push back the ink toward the common liquid chamber 104 as shown by an arrow A, and the sum of these forces is several times as large as that in a print head with a single ejection opening.
In this case, to obtain a proper refill state, a large amount of ink must be rapidly moved toward the ejection openings 101 as shown by an arrow B in FIG. 20B, and to change the ink movement direction in this manner, a pressure is required which is sufficient to overcome an initial strong inertia force (total pressure) of the ink such as that described above.
However, a capillary force of the ink which causes the refill in each liquid path 102 is insufficient to instantaneously move a large amount of ink toward the ink ejection openings 101 against the total pressure toward the common liquid chamber 104. That is, as the above described initial inertia force during the ink movement increases, a larger amount of time is required to allow a meniscus 106 to recover. Then, if the ejection frequency is reduced to allow for the sufficient amount of time for the meniscus recovery, a printing speed will decline. On the other hand, if a sufficient amount of time cannot be allowed for the meniscus recovery, printing will be inappropriate, for example, a predetermined amount of ejected ink droplets are not obtained, as described above. In particular, such a phenomenon is known to be particularly significant at the beginning of printing.
FIGS. 21A and 21B are diagrams useful in explaining a mechanism of the above-described phenomenon. FIG. 21A is a diagram showing a meniscus move back curve, and FIG. 21B is a diagram showing a general configuration of the ink ejection opening and its neighborhoods.
The amount of meniscus move back (Lxcexcm) indicated on an axis of ordinate in FIG. 21A is expressed in terms of a length L measured from an end of the ejection opening 101 in the liquid path 102 as shown in FIG. 21B, and particularly corresponds to a distance between the ejection opening 101 and the furthest point to which the meniscus has receded.
For example, in the print head with a single ejection opening, the meniscus 106 formed in the liquid path 102 near the ink ejection opening at a point of time t0xe2x80x2, which is a point of time after a certain amount of time from a point of time t0 when energy from the ejection energy generator 103 is applied to the ink in the liquid path 102, that is, at the point of time when ink ejection is performed, rapidly starts to recede, as shown by the curve labeled CM1 in FIG. 21A. The amount of move back reaches its maximum value at a point of time t1xe2x80x2 and this value is relatively large. Subsequently, a recovery force based on the capillary force causes the meniscus 106 to return to its original position, and refill is completed at a point of time t1.
On the contrary, in the print head with a large amount of ink ejection openings, as shown by a curve CM2, the maximum amount of move back at t1xe2x80x2 is smaller than that in the above described case, whereas a refill speed is lower as indicated by a move back completion time t2.
This is because the sum of pressures that push the ink from the large number of liquid paths 102 backward substantially exceeds the pressure that allows the ink to flow in the common liquid chamber 104 and because a portion of the sum which exceeds the latter pressure acts on the ink to significantly reduce the initial refill speed at which the meniscus 106 recovers.
Such a phenomenon is unlikely to occur after continuously repeated ejection because a steady flow of the ink from an ink supply tube 105 (see FIGS. 20A, 20B) to the common liquid chamber 104 has been formed. However, it is significant at the beginning of ejection, particularly, significant between the start of the ejection and a time at which about 200 times of ejection operation are performed to cause the ink flow to become steady.
In this case, the decrease in refill speed in the print head 110 with the large number of ink ejection openings 101 as described above poses no problem when a period used to apply a printing signal to the ejection energy generator 103 is set to be longer than the period between the points of time t0 and t2 shown in FIG. 21A. However, when a subsequent signal is applied in a period shorter than the period between the points of time t0 and t2 so that the refill has not been completed, for example, when the amount that the meniscus has receded is still 30 xcexcm or more for high-speed printing, a decrease in the amount of ejected ink droplets or the like may occur as described above to prevent proper printing.
Known means for solving these problems include a configuration provided with an open section to atmosphere in the common liquid chamber near the liquid path to absorb the pressure acting toward the common liquid chamber during ink ejection, as disclosed, for example, in U.S. Pat. No. 4,578,687. In this configuration, however, the common liquid chamber is open to the atmosphere, so that solvent components of the ink evaporate to make the ink in the print head more viscous or precipitate solids within the ink to block the liquid path and the ejection opening, resulting in frequent improper printing. Furthermore, vibration or the like may cause bubbles to be generated in the liquid chamber or a special design may be required to prevent dust or the like from entering the print head through the atmosphere open section. Therefore, this configuration is insufficiently practical.
Incidentally, the ejection energy generating elements such as an electro-mechanical converting element and an electro-thermal converting element (thermal energy generation resistor), which are well known, are put in practical use in an ink-jet printing. Among them, a bubble jet method using the electro-thermal converting element, which heats a liquid contacting thereto so as to evaporate the liquid for making the bubble during extremely short time, shows a following behavior of the ink with respect to the refill. A part of the liquid (mainly the liquid disposed in an ejection opening side of a liquid path including the electro-converting element) is pressed to move towards the ejection opening and other liquid in the liquid path is pressed to move towards an ink supply path. The bubble forms an interface between a liquid and a gas on the above behavior. Accordingly, when continuous ink ejection is performed, generation and disappearance of the bubble at a high frequency cause a movement of the liquid. Many proposals such as providing a dummy nozzle and a dummy hole have been made with respect to the refill in order to dissolve a problem of the high frequency vibration of the liquid.
On the other hand, as an ejection method of the bubble jet method, two kinds of ejection methods are known. Respective behaviors of the refill will be explained as follows, correspondingly to respective ejection methods.
Move Back and Return of the Meniscus in an Ordinary Ejection Method of the Bubble Jet Method
Upon a process in which a liquid droplet is formed from the liquid and is ejected, a front surface of the liquid remaining in a nozzle forms the meniscus. Upon a process in which the bubble is disappeared, the meniscus formed at the front surface of the liquid is moved back in a retracting manner by an action of the disappearance of the bubble. At the same time, the interface between the gas and the liquid, which is formed as a back boundary part of the bubble, is moved towards the front also by the action of the disappearance of the bubble. That is, the process of the disappearance of the bubble per se functions as a part of driving force for making the interface positioned at the back of the electro-thermal converting element and the liquid contacted thereto return to the front of the nozzle.
Move Back and Return of the Meniscus in an Ejection Method of so Called Bubble Through Jet Type
This method is featured that the bubble generated by the thermal energy caused by the electro-thermal converting element communicates with an air before the liquid droplet is ejected from the nozzle. Accordingly, the process for disappearance of the bubble described above does not exist and the interface between the gas and the liquid as back boundary part of the bubble forms the meniscus which has been moved back. At a front of the meniscus moved back, an area of the air, whose pressure is substantially the same as that of atmosphere, is formed. The meniscus returns to the front of the nozzle with pressing the air (having substantially the pressure of the atmosphere). According to a consideration with respect to a printing head having the liquid path of the same dimension to the printing head of the ordinary ejection method, since the action accompanied with the disappearance of the bubble does not exist when the meniscus returns to the front, the refill is performed by a capillary force of the liquid path.
Following two prior arts are known as arts regarding ink supply in the printing head of the above described bubble jet type.
Japanese Patent Application Laid-open No. 10-305592 (1998) discloses relatively large chamber provided for receiving fine bubbles which is disposed around an ink supply path. Fine bubbles separated from the bubble for ejection become so many in a liquid chamber and then ejection failure may be caused. An ordinary method performs a suction recovery operation for preventing the ejection failure due to the fine bubbles from being caused. In contrast, the prior art provides the large chamber for receiving the fine bubbles. The chamber has only the liquid therein at beginning of use of a printing head. Then, the fine bubbles increase in the chamber with use of the head and when the chamber is filled with the fine bubbles the head integrally having an ink tank is exchanged by new one for preventing the liquid supply path from receiving the fine bubbles.
Japanese Patent Application Laid-open No. 6-210872 (1994) discloses that an air chamber (a buffer chamber) is provide at an opposite and back side to nozzles with respect to a common chamber. Providing the buffer chamber near the nozzles allows a vibration (high frequency vibration) of a liquid caused by driving for ejection, generating the bubble and ejection of the respective nozzles to be decreased so as to prevent ejection of other nozzle from being affected. That is, the prior art discloses prevention of a crosstalk.
The prior art also discloses that a head unit, a ink supply tube for supplying ink to the head unit and an air chamber formed at a connection portion between the head unit and the ink supply tube are provided along a path from an ink tank section to a head section. Especially in FIG. 12 of the prior art, the air chamber is formed around the ink supply tube having constant section area.
An first object of the present invention is to improve a function of an air buffer which eliminates or decreases an effect of a vibration of a liquid caused along a liquid supply path from an ink supply source (an ink tank and the like) to a head chip (including a plurality of liquid path and a liquid chamber) comprising a liquid ejection element like a prior art, among vibrations of liquid caused in a printing head.
The present invention is made especially by considering an arrangement of the air buffer as well as a configuration of the air buffer and a relation between the air buffer and surrounding elements.
A second object of the present invention is to eliminate or decrease an effect of a low frequency vibration of a liquid upon an ejection behavior. This object is based on following consideration. In a bubble through jet method, the low frequency vibration may affect a capillary force which functions as a driving force for a refill of a liquid so that the refill is performed insufficiently or is performed too much to cause ejection failure.
Further object of the present invention is to provide a structure for effectively manufacturing an air buffer.
In a first aspect of the present invention, there is provided a print head comprising:
a print element substrate having a substrate on which an ejection energy generating element for generating thermal energy that is used for ejecting ink is provided, and an ejection opening plate which is provided on the substrate and in which an ejection opening is provided so that the ejection opening faces the ejection energy generating element; and
a support member being contact with the substrate to support the print element substrate,
wherein an ink supply path for supplying the ink to the ejection opening on print element substrate, and
an air chamber communicating the ink supply path and including an air are provided, and
at least a part of inner wall of the air chamber is formed with the support member.
In a second aspect of the present invention, there is provided an ink jet printing apparatus comprising:
a print head including:
a print element substrate having a substrate on which an ejection energy generating element for generating thermal energy that is used for ejecting ink is provided, and an ejection opening plate which is provided on the substrate and in which an ejection opening is provided so that the ejection opening faces the ejection energy generating element; and
a support member being contact with the substrate to support the print element substrate,
wherein an ink supply path for supplying the ink to the ejection opening on print element substrate, and
an air chamber communicating the ink supply path and including an air are provided, and
at least a part of inner wall of the air chamber is formed with the support member; and
In a third aspect of the present invention, there is provided an ink jet head comprising:
a head chip including a plate which is provided with a plurality of liquid flow paths, liquid ejection elements corresponding to the plurality of liquid flow paths respectively and liquid ejection opening corresponding to the liquid ejection elements respectively, and in which a through hole space receiving a liquid is formed; and
a liquid supply unit having a liquid supply path for supplying the liquid from a liquid supply source to the head chip,
wherein the plurality of liquid flow paths are arranged as a group in the head chip, and a communication portion communicating with the liquid supply path and forming an interface between a gas and a liquid and a gas retaining chamber which has larger volume than that of the communication portion and retains a gas, are provided at one end and another end of the group.
In a fourth aspect of the present invention, there is provided an ink jet head comprising:
a head chip including a plate which is provided with a plurality of liquid flow paths, liquid ejection elements corresponding to the plurality of liquid flow paths respectively and liquid ejection opening corresponding to the liquid ejection elements respectively, and in which a through hole space receiving a liquid is formed; and
a liquid supply unit having a liquid supply path which supplies the liquid from a liquid supply source to the head chip and has inclined portion,
wherein a gas retaining chamber retaining a gas is disposed at a position capable of receiving a component of liquid movement of a different direction, which is caused by the inclined portion of the liquid supply path, from a direction of liquid supply.
In a fifth aspect of the present invention, there is provided an ink jet head comprising:
a head chip including a plate which is provided with a plurality of liquid flow paths, liquid ejection elements corresponding to the plurality of liquid flow paths respectively and liquid ejection opening corresponding to the liquid ejection elements respectively, and in which a through hole space which has an inclined portion and receive a liquid is formed; and
a liquid supply unit having a liquid supply path which supplies the liquid from a liquid supply source to the head chip and has inclined portion,
wherein a gas retaining chamber retaining a gas is disposed near a position where an elongated line of the inclined portion of the through hole space crosses an elongated line of the inclined portion of the liquid supply path.
In a sixth aspect of the present invention, there is provided an ink jet head comprising:
a head chip including a plate which is provided with a plurality of liquid flow paths, liquid ejection elements corresponding to the plurality of liquid flow paths respectively and liquid ejection opening corresponding to the liquid ejection elements respectively, and in which a through hole space which has an inclined portion and receive a liquid is formed; and
a liquid supply unit having a liquid supply path which supplies the liquid from a liquid supply source to the head chip and has inclined portion,
wherein a gas retaining chamber retaining a gas is disposed at a position which a surface of the inclined portion of the through hole space and a surface of the inclined portion of the liquid supply path face respectively.
According to the above configuration, the air chambers, which communicates with the ink supply chamber common to the plurality of ink ejection openings for supplying the ink to these ink ejection openings and to which the pressure is transmitted from the ink supply chamber, is provided. Accordingly, the pressure caused upon ejection of the ink in each ejection opening and propagated to the ink supply chamber also propagates to the air chamber as a change in the pressure of the air in the air chamber and is absorbed due to a compression of an air in the air chamber.
In addition, since the air chambers are provided at the opposite side of the ejection openings with respect to the print element substrate, the air chamber does not communicate with the atmosphere, thereby preventing the ink in the print head from being made more viscous through the air chambers.
Furthermore, since an inner wall of the air chamber is formed with the support member, the air chamber can be disposed at an area relatively nearer to a portion for ink ejection.
When two members at lest of which has a recess are connected to each other in a manner that the recess is position at connection face side, the air chamber of a seal structure can be easily manufactured.
The air chamber communicates with the ink supply path at end of an inclined portion of an inner wall of a through hole forming the ink supply path so that a buffer action caused by the inclined portion and a buffer action caused by the air chamber meet to provide further stable ink supply characteristic.
The ink supply path has a bend portion at an upper stream side than the air chamber so that a buffer action caused by the bend portion and the buffer action caused by the air chamber meet to provide further stable ink supply characteristic.
In addition, in a bubble through jet method, the buffer action caused by the air chamber can be more effectively shown to realize high level of the buffer action.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.